Method for making lithium nickel ferrite having a substantially rectangular hysteresis loop



United States Patent 4 Claims. cr. 252-4225 Our invention relates to a ferromagnetic body having a substantially rectangular hysteresis loop for use as a memory element, and to a method of manufacturing such a body. Memory elements are used, for example, in electronic computers.

It is desirable to restrict the occurrence of eddy currents in memory elements as much as possible. Consequently, increasing use is made of ferromagnetic soft oxidlc materials, which as is known, have a very small electric conductivity.

The utility of such cores as memory elements is based upon a significant difference between the zero signal" and the one signal (in the computer technology the zero or undisturbed one signal, uVl, is distinguished from the one or disturbed one signal, rVl; however, in a good memory element these quantities differ only slightly from one another). Consequently, it is necessary, in addition to sufiicient rectangularity of the hysteresis loop that, for a given rise time of the control current, the lapse of time between the beginning of the control current pulse and the point of time at which the output voltage of the one signal reaches a strength of of its maximum value is substantially constant. The peak time (T of a magnetic core is understood to mean the lapse of time between the point of time at which the control current reaches a strength of 16% of its maximum value and the point of time at which the output voltage of the one signal, which is produced by a control current pulse, has become a maximum. The peak time naturally depends upon the rise time (T of the control current pulse. Preferably the rise time should always be about 0.15 micro-second.

Variations in the current pulse characteristics of memory elements which occur as a result of temperature variations have thus far in most cases been corrected by varying the strength or" the control current. Alternatively, the whole system of memory elements has been placed in a temperature-controlled environment to prevent disturbing temperature variations. However, these methods are complicated and cumbersome. In addition, they are useless if during operation of the system temperature differences occur between the individual memory elements because one element is switched a greater number of times in a given lapse of time than the other. It, therefore, is of great importance to have memory elements which not only have a sufiiciently large squareness ratio, but also for which the output voltage of the one signal, and also the peak time, are only slightly dependent on the temperature over a Wide temperature range (preferably between -50 C. and +12il (1.).

It is an object of our invention to provide a ferromagnetic body having a substantially rectangular hysteresis loop for use as a memory element.

It is a further object of our invention to provide a new and novel ferromagnetic ferrite which exhibits a substantially rectangular hysteresis loop which is substantially less temperature dependent.

Another object of our invention is to provide a ferromagnetic ferrite body suitable for use as a memory Patented Dec. 28, 1965 element which has a peak rise time substantially independent of temperature over a wide range of temperatures.

These and further objects of our invention will appear as the specification progresses.

in accordance with the invention, we have found that ferromagnetic bodies having a substantially rectangular hysteresis loop and which have peak rise times substantially independent of temperature over a wide range of temperatures when used as memory cores can be manufactured by mixing lithium oxide, nickel oxide, and ferric oxide in the proportions of about 2 to 20 mol percent of Li -O, about 0.5 to 45 mol percent NiO, and about 50 to mol percent Fe O and after compacting the mixture to form a body, heating the mixture at a temperature of about 1200" to 1400 C. in an atmosphere containing at least as much oxygen as air.

In addition to the constituents Li O, NiO and Fe O the mixture may also include up to 3 mol percent of ZnO, and up to 8 mol percent C110. Further, instead of oxides of these metals, compounds which are converted by heating into oxides may be used. In order to insure a more homogeneous product, it may be desirable to reduce the heated product, after cooling, to a powder and reheating. The product may be reduced to powder several times and heated several times.

In a preferred embodiment, the mixture is heated at a temperature of about 1200 to 1400 C. after which it is first cooled at a rate of not more than 30 C. per minute to a temperature which is to 600 C. below the heating temperature and is then quenched or, if the mixture which is heated at a temperature of about 1200 to 1400" C. is cooled at a rate of more than 30 C. per minute to a temperature which is 100 to 600 C. below the heating temperature, is maintained at this lower temperature for at least five minutes and then quenched.

The preferred composition of the cores for which optirum properties may be realized is in a range of compositions in which the oxides of lithium, nickel and iron correspond to 14-15 mol percent Li O, 5--7 mol percent NiO, and 7880 mol percent F5203.

it should be noted that although lithium-nickel ferrite cores having a substantially rectangular hysteresis loop are known which are manufactured by heating at a temperature of from 1100 to 1200" C., they are less suitable as memory elements than those manufactured accordin to the present invention. More particularly, when used as memory cores, the difference between the output voltage of the zero signal and that of the one signal is significantly smaller. It was believed heretofore that the volatility of the lithium oxide handicapped the use of heating temperatures higher than 1200 C. It has appeared, however, that this is not the case provided that it is ensured that the sintering takes place in a gas atmosphere which contains very little, if any, water vapour.

The following examples are illustrations of the invention which is defined in the appended claims.

Mixtures of lithium carbonate, Li CO nickel carbonate, N-iCO iron oxide, Fe O and, if desired, zinc oxide, ZnO, and copper oxide, CuO were ground in ethanol in a ball mill for four hours The ground products were presintered in air, cooled to room temperature and ground in ethanol in a ball mill for 16 hours. The resulting ground products, after the addition of an organic binding agent, were granulated and compacted into rings, at a pressure of 1.5 ton/ch1 having an outside diameter of 1.63 mm., an inside diameter of 0.94 mm, and a height of 0.38 mm. These rings were heated in air by heating at a temperature between 1200 C. and 1400 C.

In some cases the pre-sintering was omitted. The following table specifies further details concerning the chemical composition and the conditions of preparing the cores as well as a number of measured results. The output voltage of the zero signal and that of the disturbed 2. A method of manufacturing a ferromagnetic body having a substantially rectangular hysteresis loop comprising the steps, forming a finely-divided mixture of about 2 to 20 mol percent of LL 0, about 0.5 to 45 mol percent one signal (rVl), as well as the peak time (T at a rise 5 N10, about 50 to 85 mol percent Fe O up to 3 mol pertime (TI) of the control current pulse of 0.15 micro-seccent of ZnO, and up to 8 mol percent of CuO, compacting end are speclfied for all compositions. All the measuresaid mixture into a body, heating sald body to a temperaments were carrled out at 25 C. For some cores, the ture of about 1200 to 1400 C. 1n an atmosphere substantemperature coefficients of the undlsturbed one signal tially free of Water-vapor containing at least as much (uVl) and of the peak time (T are also specified. 10 oxygen by volume as air, coohng said body from said TABLE I Composition in mol percents of the oxides Presintering (llqpre temperature Way of sintering and cooling LiO NiO ZnO CuO F620;

1 15.43 5. 35 79. 22 800 Passed through the furnace at arate of 2 cm. per minute. In the heating zone of the furnace, 8 ems. long, a temperature of l,243 C. prevailed. 2 14. 55 6. 45 79. O 750 Passed through the furnace at arate of 2 cm. per minute. In the heating zone of the furnace, 8 ems. long, a temperature of 1,250 0. prevailed. 3 15. 76 4.04 80. 2 800 Heated at 1,258 C. for 10 minutes, cooled within the furnace to 1,000

C. and then quenched. 4 16. 3 1. 2 82. 5 750 Heated at 1,340 C. for 5 minutes, cooled Within the furnace to 900 C.

and then quenched. 5 14. 55 6.45 79.0 750 Heated at 1,340 C. for 10 minutes, cooled within the furnace to 1,000

C. and then quenched. 6 14. 55 6. 45 79. 625 Heated at 1,280 O. for minutes, rapidly cooled to 980 0., maintained at 980 C. for 15 minutes and then quenched. 7 14. 55 6.45 79.0 Heated at 1,340 C. for 5 minutes, cooled within the furnace to 1,000 C.

and then quenched. 8 14.55 6. 45 79.0 Heated at 1,350 0. for 5 minutes, rapidly cooled to 1,020 0., maintained at 1,020 O. for minutes and then quenched. 9 14. 55 5. 45 1.0 79.0 775 Heated at 1,337" O. for 5 minutes, cooled within the furnace to 1,000 O.

and then quenched. 10 14. 55 4. 45 2.0 79.0 775 Heated at 1.35080. for 5 minutes, rapidly cooled to 1,100 0, maintained at 1,100 O. for 40 minutes and then quenched. 11 8. 8 17. 7 5. 9 67.6 750 Heated at 1,340 O. for 5 minutes, cooled within the furnace to 970 C.

and then quenched. 12 12. 5 6.25 6.25 75. 0 750 Heated at 1,262 C. for 7 minutes, rapidly cooled to 970 0., maintained at 970 C. for minutes and then quenched. 13 15.03 5.23 79.74 900 Passed through the furnace at a rate of 2 ems. per minute. In the heating gone of the furnace, 8 ems. long, a temperature of 1,235 C. prcvai e 14 15. 43 5. 35 79. 22 800 Heated at 1,218 C. for 10 minutes, cooled Within the furnace to 1,050

O. and then quenched.

TABLE IL-MEASURED RESULTS Output volt- Output Temperature coelficient of the peak time, T Temperature coeflieient of the undusturbed Core No. age of the voltage of the Peak time. one signal, uVl

zero signal disturbed T (micro- (millivolts) one signal, seconds) TVl (milli- Percent per In the temp. range from- Percent per In the temp. range fromvolts) C. C.

14 42 0.33 0. 0 +25 C. to +60 C 0.56 +25 C. to +60 C. 32 85 O. 58 13 48 9. 43 0. 0 0. 6 C. to +60 C. 14 64 0.44 18 94 0.33 0.0 40 C. to +140 0 0. 53 -40 C. to +160 C. 108 0.27 29 114 0. 26 36 118 0. 26 14 61 0.6 0.0 10 C. to +100 O 0. 55 --40 C. to +160 0. 18 40 0. 5 95 225 0.23 110 230 0. 22

14 31 0. 3 0. 0 +20 C. to +60 C 0. 46 +20 C. to +60 C. 15 48 0. 44 0.0 +20 C. to +00 C 0. 49 +20 0 to +60 C.

While we have described our invention in connection with specific embodiments and applications thereof, other modifications will thus be apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. A method of manufacturing a ferromagnetic body having a substantially rectangular hysteresis loop comprising the steps, forming a finely-divided mixture of about 2 to 20 mol percent of Li O, about 0.5 to mol percent NiO, about 50 to 85 mol percent Fe O up to 3 mol percent of ZnO, and up to 8 mol percent of CuO, compacting said mixture into a body, heating said body to a temperature of about 1200 to 1400 C. in an atmosphere substantially free of water-vapor containing at least as much oxygen by volume as air, cooling said body from said heating temperature to a temperature of about 100 to 600 C. below the heating temperature at a rate of not more than 30 C. per minute, and quenching said body fromthe temperature to which it was cooled.

heating temperature to a temperature which is 100 to 600 C. lower than said heating temperature at a'rate which is greater than 30 C. per minute maintaining said body at said latter temperature for at least five minutes, and quenching said body from said latter temperature.

3. A method of manufacturing a ferromagnetic body having a substantially rectangular hysteresis loop comprising the steps, forming a finely-divided mixture of about 14 to 15 mol percent of M 0, about 5 to 7 mol percent NiO, about 78 to 80 mol percent Fe O compacting said mixture int-o a body, heating said body to a temperature of about 1200 to 1400 C. in an atmosphere substantially free of water-vapor and containing at least as much oxygen by volume as air, cooling said body from said heating temperature to a temperature about to 600 C. below said heating temperature at a rate of not more than 30 C. per minute, and quenching said body from said latter temperature.

4. A method of manufacturing a ferromagnetic body having a substantially rectangular hysteresis loop com- 5 prising the steps, forming a finely-divided mixture of about 14 to 15 mol percent of Li O, about 4 to 7 mol perpercent NiO, about 78 to 80 mol percent Fe O compacting said mixture into a body, heating said body to a temperature of about 1200 to 1400 C. in an atmosphere substantially free of Water-vapor and containing at least as much oxygen by volume as air, cooling said body from said heating temperature to a temperature about 100 to 600 C. below said heating temperature at a rate greater than 30 C. per minute, maintaining said body at said latter temperature for at least five minutes,

and quenching said body from said latter temperature.

References Cited by the Examiner TOBIAS E. LEVOW, Primary Examiner.

10 MAURICE A. BRINDISI, Examiner. 

1. A METHOD OF MANUFACTURING A FERROMAGNETIC BODY HAVING A SUBSTANTIALLY RECTANGULAR HYSTEREIS LOOP COMPRISING THE SSTEPS, FORMING A FINELY-DIVIDED MIXTURE OF ABOUT 2 TO 20 MOL PERCENT OF LI2O, AND ABOUT 0.5 TO 45 MOL PERCENT NIO, ABOUT 50 TO 85 MOL PERCENT FE2O2, UP TO 3 MOL PERCENT OFZNO, AND UP TO 8 MOL PERCENT OF CUO, COMPACTING SAID MIXTURE INTO A BODY, HEATING SAID BODY TO A TEMPERATURE OF ABOUT 1200* TO 1400*C. IN AN ATMOSPHERE SUBSTANTIALLY FREE OF WATER-VAPOR CONTAINING AT LEAST AS MUCH OXYGEN BY VOLUME AS AIR, COOLING SAID BODY FROM SAID HEATING TEMPERATURE TO A TEMPERATURE OF ABOUT 100* TO 600*C. BELOW THE HEATING TEMPERATURE AT A RATE OF NOT MORE THAN 30*C. PER MINUTE, AND QUENCHING SAID BODY FROM THE TEMPERATURE TO WHICH IT WAS COOLED.
 2. A METHOD OF MANUFACTURING A FERROMAGNETIC BODY HAVING A SUBSTANTIALLY RECTANGULAR HYTERSIS LOOP COMPRISING THE STEPS, FORMING A FINELY-DIVIDED MIXTURE OF ABOUT 2 TO 20 MOL PERCENT OF LI2O, ABOUT 0.5 TO 45 MOL PERCENT NIO, ABOUT 50 TO 85 MOL PERCENT FE2O3, UP TO 3 MOL PERCENT OF ZNO, AND UP TO 8 MOL PERCENT OF CUO, COMPACTING SAID MIXTURE INTO A BODY, HEATING SAID BODY TO A TEMPERATURE OF ABOUT 1200* TO 1400*C. IN AN ATMOSPHERE SUBSTANTIALLY FREE OF WATER-VAPOR CONTAINING AT LEAST AS MUCH OXYGEN BY VOLUME AS AIR, COOLING SAID BODY FROM SAID HEATING TEMPERATURE TO A TEMPERATURE WHICH IS 100* TO 600*C. LOWER THAN SAID HEATING TEMPERATURE AT A RATE WHICH IS GREATER THAN 30*C. PER MINUTE MAINTAINING SAID BODY AT SAID LATTER TEMPERATURE FOR AT LEAST FIVE MINUTES, AND QUENCHING SAID BODY FROM SAID LATTER TEMPERATURE. 